Heretofore, a stop valve has been provided in a passage connecting to a high-pressure gas tank. Unexamined Japanese Patent Publication No. 9-210296 discloses an example of such a stop valve in which a male screw thread formed on a valve element is threadably screwed into a female screw thread formed inside a valve body. The valve element is exposed to the outside of the valve body and can be manually operated by a driving tool from the outside (i.e., external to the valve body). The valve element is driven back and forth in an axial direction by a rotating operation of the valve element. In addition to the movement, the rotating operation causes the valve element to be attached to and detached from a valve seat provided within a passage, thus opening and closing the passage. In order to prevent a leak of high-pressure gas, an annular sealing member, such as an O-ring made from an elastic material, is provided on the outer circumferential surface of the valve element. The sealing member is arranged to be brought into sliding contact with the inner circumferential surface of a cylindrical shape located at a non-threaded portion inside the valve body.
In recent years, further increases in gas filling pressures, for example from 35 MPa to 70 MPa, have been desired when filling high-pressure hydrogen gas into the gas tank of a fuel cell vehicle. However, in the aforementioned conventional stop valve, the valve element is rotated clockwise and counterclockwise by the rotation caused by the male screw being threadably screwed into and out of the female screw thread inside of the valve body. Along with the rotation of the valve element, the sealing member is also rotated clockwise and counterclockwise in the same manner. Accordingly, sealing performance of the sealing member is deteriorated due to the distortion resulting from the rotation. In the case that the gas filling pressure is set to a higher level than before, there is a fear that a leak of hydrogen gas may occur.